1. Field of the Invention
The invention relates to the field of fluid flow measuring devices and, more particularly, to a fluid strainer and flow corrector for use with such flow measurement devices.
2. Description of the Prior Art
Fluid flow measuring devices, such as turbine type fluid flow meters, often use strainers and/or flow correction devices arranged ahead of the inlet of the flow meter. Strainers generally take the form of a flat plate of material, such as stainless steel, having a series of regularly spaced openings arranged in a mesh or grid pattern. The size of the openings is arranged to be on the order of or less than the size of the smallest particles or debris which may be present in the fluid which the flow meter is designed to measure. Since the accumulation of debris on the strainer eventually builds up to the point where it must be removed, such straining devices must be mounted in a way which enables them to be readily moved from the flow meter. This is often done by simply bolting the plate-like strainer between a flange provided on the inlet side of the flow meter housing and the pipe or other conduit to which the inlet side of the flow meter is connected. Of course, such an arrangement requires a good compression seal between the inlet flange of the flow meter and the flange of the pipe to which it is connected. Furthermore, the flow meter must be temporarily disconnected from the pipework to allow the strainer to be cleaned or replaced.
It is also known to mount a so-called "strainer box" upstream of the flow meter housing. The strainer box includes a mesh-type strainer element which is removable through a cover provided on the strainer box. This arrangement allows the strainer element to be removed without the need to disassemble the pipework connected to the strainer box and flow meter.
In addition to a debris strainer, fluid flow meters also often employ fluid flow correction devices. Such flow correction devices can take the form of a series of spaced-apart vanes arranged parallel to the diameter of the flow meter inlet, with the vanes being relatively thin and arranged in planes which are parallel to the longitudinal access of the inlet of the flow meter, i.e. substantially parallel to the direction of the fluidflow. Another type of flow correction device is comprised of a bundle of tubes disposed upstream of the flow meter inlet with the longitudinal axis of each such tube arranged parallel to each other and to the direction of fluid flow.
Such fluid flow correction devices are designed to impart a desired velocity profile to the fluid and/or correct swirling (rotation of the fluid about the direction of flow). As is well known, the velocity of the fluid in a tubular conduit or pipe free of obstructions is generally higher in the center of a conduit (i.e. along the longitudinal axis of the conduit) than at points closer to the wall of the conduit. However, for many types of fluid flow meters, such as turbine flow meters, it is desirable to have a substantially uniform fluid flow velocity profile at all points in a plane perpendicular to the longitudinal axis of the conduit. This enables the flow sensing element of the flow meter to give as accurate a reading as possible of the velocity and/or quantity of fluid flowing past the element.
Fluid flow correction devices of the type described above must be mounted upstream of the flow meter inlet and any debris strainer. Such flow correction devices normally require that a straight section of pipe be provided ahead of the flow correction device. The straight length of pipe generally must be at least several pipe diameters long in order to provide non-turbulent fluid flow conditions ahead of the flow corrector to ensure optimum flow correction. This requirement restricts the use of such flow correction devices to environments where such a straight piping run can be provided immediately ahead of the flow meter inlet. Unfortunately, such an arrangement is not always practical due to space limitations, existing piping configurations, etc.
It is also known to utilize a strainer of the flat-plate type described above as a flow correction device. For example, the size and/or spacing of the openings further from the center of the strainer can be made greater relative to those closer to the center of the strainer in order to impart a desired fluid flow velocity profile. However, such devices still require a compression seal between the flow meter inlet flange and the flange of the piping connected to the flow meter, and require that the flow meter be temporarily disconnected from its pipework in order to clean or replace the strainer.
It would be desirable to have a combination strainer and fluid flow corrector which is easy to mount and dismount from the inlet of a flow meter without requiring a special housing or disconnection of the flow meter from its pipework and which does not require long straight piping runs ahead of the inlet, while still providing the desired straining and fluid flow velocity profile correction to the fluid.